Heat exchanger



P 1952 c. BOLING 2,611,587

HEAT EXCHANGER F e y 27, 1950 I 4,,Sheets-Sheet 1 INVENTOR Ceqil Balic." BOLING HEAT EXCHANGER Sept. 23, 1952 Filed July 27, 1950 l mi Q J Afin mw. m QN QM... Q h m r hm W'IML mm .wmuw m H q NS. No Q0. I 3 mm. #9F NR QM Q Q 5 a mm w N m mm 5 I mm R @N l Mw m on v @N $9 m QB In Q l wi Q wm QQ MI HE mm m mm. mm. Q% g QINI QM. w l %Q\ NM. ya w Lu \W n 4. wm0 4N vR 0 ma n C A 6 MM Sept. 23,1952 c. BOLING 2,611587 HEAT'EXCHANGER7 Filed- July 2'7, 1950 4- Sheets-Sheet;3

INVENTOR C'ecil Balin Sept; 23, 1952' c, BOLlNG 2,611,587

HEAT EXCHANGER Filed July 27, 1950 4-'5 h06tS-$h99t 4 sag N I xi '3ENVENTOR C'ecLl Bolizy Patented Sept. 23, 1952 UNITED STATES PATENTOFFICE];

.Heat-X-Qha er 00., In 6., Brewster, N. an, a corporation .of ew' YorkApplication 'July -27, 1950, SerialNo. "176,128

"Thisinvention relates :t'orefrigeration :and heat transfer for exchangeequipment :such as that which is used in refrigeration systems, withsuch equipment, and more in particular to improved refrigeration systemsand :heat exchange components :such as condensers, 'evaporators land theilike where one afiuidvis passed into heat exchange relationshi with'one-ormore otherfluids.

- object of thisdnvention is to provide improved refrigeration systemswherein extremely efficient operation is obtained "with equipmentr-which is simple and sturdy in construction, inexpensive to manufactureand maintain, compact, flight inweight and'thoroughly dependable in use,and which :is adaptable "to .meet many problems indifferent fields.Further obj'ectsare to provide improved heat exchange units havingcertain or all of the above desirable characteristics with particularattention being directed toward providing improved condensers,evaporators and :the "like. Aifnrther objecttis to provide heat exchangeequipment which may be of more. or less standardized design andconstruction and yet which is adaptable for use in solvingmanydifferent'prob :lems which have been encountered in widely diversifiedfields. A still further object is to provide .for the manufacture ofequipment of the above character upon :a mass production basis with theadvantages and economies whichmay be obtained thereby. :Ihese and otherobject will be in part obvious and in part pointed out below.

The invention accordingly consists in the features of construction,combinations of elements, arrangements of :parts and in the severalsteps and relation and order "of each of the same .to one. or more ofthe others, all as will be illustra- -tively described herein, and thescope of the application .of which "will :be indicatedin the "followingclaims.

In :the'drawings: Figure l is a somewhat schematic representation ofoneembodirnent of the invention;

v Figure 71,; and,

:5 Claims. (C1. 325F247) 2- ,4 Figure 1051s a section onwthe line [0-40,ofaFiE- 'ure 9.

Refrigeration systems generally :include tw-o1or more heat transferunits wherein heat is transferred to. or from :a .streamor streams ofthe re-- frigeratlng :medium. Examples .of such heat transfer units are:condensers, evaporators and heat changers where one stream ofrefrigerant is passed in :heat transferrel-ationship with another orwhere a :liquid or air is cooled or heated by a liquid or .gas. With anyparticular refrigeration system the performance may be improved "byincreasing the rate of heat transfer at the heat transfer units. "Thus,if there is a high-rate of heat transfer .at the condenser, a relativelylarge amount of refrigerant is condensed with a minimum amount ofrairjorwater and-with a relatively small condenser. Similarly, the performanceof the system is'im-proved by increasing the rate of heat transfer tothe refrigerant in the evaporator, thus, .to promote uniform coolingthroughout;the evaporator zone and uniform and completeevaporation ofthe refrigerant.

Generally, the performance of an air cooled condenser varies over arelative1y wide rang in accordance with the ambient temperature aswellas the load. That is, the rate at which heat is transferred from thecondenser drops materially -when the ambient temperature rises, and ithas been accepted practice to design air cooled condensers forrefrigerationsystems with a relatively high excess load factorat normalo mean ambient temperatures solely to take care of the high loads :at:high ambient temperatures. Proposals have been made to provide both anair-cooled condenser and a water "cooled condenser for a singlerefrigeration'system or to utilize bothair and water to cool a singlecondenser unit. With such arrangements most or all of the heatis passedto the air at light loads and at low ambient temperatures, but as theambient temperature or the load rises, ,heat is passed-to the water.How- 'ever, it has been idifficult to provide for the efficient transferof heat to both air and \water with condenser structure which isinexpensive to .m n factur and thorou hly -satisfact yii-n-everyrespect;

3 system cools a building in summer and heating is provided in winter,it is desirable to provide a single heat transfer unit of minimum sizeand cost in each room which is the heat radiator in winter and thecooling or heat-absorbing unit in summer. In each of the systemsreferred to above, the present invention contemplates the provision ofone or more heat transfer units, each of which is adapted to pass two ormore fluids, i. e., liquids or gases, into eiiicient heat transferrelationship with each other or to pass selectivelyor simultaneously twosuch fluids into heat transfer relationship with air or the like. 7

4 tween the two tubes. In each tube assembly the refrigerant from thecompressor passes through the space 32 which acts as a condensingpassageway where the gas is cooled thereby to condense it to a liquid.

Cooling water is flowed through the passageway 34 in each inner tube28j-s'o that cooling of the refrigerant gas is obtained as a result ofheat passing through the inner tube wall to the water. The flow of wateris controlled by a metering valve 29 which is connected through apressure tube to the compressed or hot gas line from the Referringparticularly to Figure l of the drawings wherein a refrigeration systemis shown somewhat schematically, a compressor 2 is driven by a motor 4and is automatically controlled so that it compresses refrigerant anddelivers it through a hot gas line 5 to a primary condenser .6 andthence to a secondary condenser 7. The refrigerant is condensed in thecondensers and the liquid refrigerant goes to a receiver 8 and thencethrough 'a liquid line Ill and an expansion valve l2 to an evaporator[4. The refrigerant, evaporates in the evaporator and flows through aline which has a throttle valve I9 therein which does not interferewiththe flow of the refrigerant gas during the refrigeration cycle. Therefrigerant then passes through a heat exchange passageway in thesecondary condenser I, and a line 16 to the compressor.

During normal operation frost accumulates on evaporator l4 and theevaporator is defrosted by passing hot gas from the compressor directlyto the evaporator so that it does not flow through the condensers.Accordingly, the system is provided with a valve II in a bypass line i8,and this valve is opened to connect the hot gas line 5 through line I8to the inlet of evaporator M; the hot gas heats the evaporator and theice is melted free. The rise in pressure causes the throttle valve illto close and throttle the flow of refrigerant as it returns from theevaporator to the compressor throughline l5 to the heat exchangepassageway in the secondary condenser I and thence to the compressorthrough line 16. This causes the refrigerant to condense in theevaporator and it is evaporated in the secondary condenser I so that thesecondary condenser is also a re-evaporator.

In the embodiment of Figure 2 the system represented is similar to thatof Figure 1 except that: a special evaporator 19 is provided; acondenser 2| of modified form replaces the condensers 6 and 1; and, thebypass line l8 and valves l1 and I9 are omitted. In this embodiment thedefrosting operation is carried on by passing a hot liquid through aseparate passageway in the evaporator to perform the defrostingoperation. Consequently, no hot gas is passed to the evaporator, and itis unnecessary to provide for the i e-evaporation of refrigerant passingto the compressor.

Condenser 2| is of a special construction which constitutes an importantphase of the invention and now will be described more in detail; Thiscondenser is shown in Figures 4 to 8 and comprises a set of sixhorizontal mult ple-passa eway condenser tube assemblies 20 (Figure 4)rigidly mounted and interconnected at their ends by a pair of headerassemblies 22 and 24. Each of the condenser tube assemblies 20 comprisesan outer tube 26 and an inner tube 28 (see also Figure 8), having aninternal. radially-compressed, fin ascompressor and permits water toflow through the condenser" at a rate sufficient to keep the pressure ofthe compressed gas within desirable limits.

The header assemblies 22 and 24 (Figure 4) provide rigid support for thecondenser tube assemblies and are in turn supported at the bottom (seealso Figures 5 and 6) by a pair of sheet metal mounting brackets 33which are clamped in place on the-base of the machine by bolts (notshown). .The header assemblies provide .fluid connections whereby-thevarious passageways 32 are connected in series; and, at the sametime,all" of the passageways 34 are connected in series. Accordingly, headerassembly 24 is provided at the bottom with a water inlet fitting 35, andat the top with a water outlet fitting 36; andlsee Figure 5) there is atthe top a refrigerant inlet fitting 31 and at the bottom a refrigerantoutlet fitting 38.

Header assembly 24 is formed by-two interengaged vertical channels 40and 42 (see Figure 7) and a third enclosing channel 44. Channels 45 and42 form the header passageways for the inner tubes 28 while channels 42and 44 form the header passageways for the annular passageways 32 intubes 26; Accordinglyxchannel 42 is providedwith a set of flangedopenings 46 which receive the ends of tubes 28 and channel 44 isprovided with concentrically positioned flanged openings 48 whichsimilarly receive the ends of tube 46. Referring to Figured, the spacebetween channels 48 a'nd'42 is divided into four header passageways 50,52, 54 and 56 by five arch-like transverse walls 58, 60, 62,- B4 and 66which are positioned as shown in Figure 6 and provide horizontal blocksor walls between the respective header passageways; The headerpassagewavs 5B and 56 are open respectively to the ends of the top andbottom tubes 28 while each of passageways 52. and 54 is open to the endsof a pair of the centrally positioned tubes 28 (see also Figure 4)Referring to Figure 5, the header passa eways 68. Ill, 12 and 74 betweenchannels 42 and 44 are similarly formed by arch-like transverse walls16, 18, 80, 82 and 84. The top and bottom passageways 68 and 10 areconnected respectively to the annular passageways 32 in the top andbottom tube assemblies while the passageways i0 and 12 are eachconnected to a pair of the centrally positioned passageways 32.

Referring to the left-hand portion of Figure 4, header 22 issubstantially identical in construction with header 24 except thatarch-like transverse walls 86 and 88 are positioned to provide: headerpassageways 90, 92 and 94 which connect the an nular passageways 32 inthe lower pair oftubes, the central pair of tubes and the top pair oftubes, respectively; and header passageways 96, 98 and I00 which connectthe ends of the lower pair of tubes 28, the central pair of these tubesand the. top pair of these tubes. It is thus seen that the water inletfitting as is connected to a ater passageway extends through. pasgewayfis; the lowertube'ze; passageway 96', the

no t tube 28, passagewaysmne next tube as; passage'ay 9a,; the tube 28;passageway 52, the

neat tube as, passa eway! flog the top tubezit-and thence throughpassageway 50' to the water outvid'ed from the refrigerant inlet fitting3 1 at the and-through passageways 6'8, 32} 9'4,- 3 2, 10,32, 92, 32',I2, 32", 9t, 32, and 14 to therefrigerant thread d into the to andbottom of these o enin-gs Hi2 and the'othe'r of these openings areclosed by a screw cap l-il l thewater' circuit may be readily cleanedbyremoving these 7 fittings and screw caps, and by inserting a spiral tubecleaner. 7 I v V The various elements of the header assemblies areconnected to each other and to tubes 26 and 28 by a soldering operation.Thus, during manufactors the elements are'assembledin a jig, and

the headers are then heated and soldered. Upon cooling the entire unitis held tog'ether as a unitary structure, and the joints and seams aresealed.

The fin assembly 36 is of. the type disclosed in copjendingflapplication Serial No. 17,899, filed IS/[arch 30, 1948, and ischaracterized by being formed'of sheet metal which is somewhatcorrugated so that fins are provided extending longiboth tubes, andgives structural advantages.

During construction of the apparatus, the fin assembly 38 and theinner'tube 28 are slid into tube is, and tube 22 is then expanded sothat it presses radially outwardly upon the fin assembly 38; Thus, eachof the fin portions lliii is com pressed radially so that one edge ispressed at a bendl l against the outer surfaceof tubs-:28 and 'theotheredge is pressed at a bend H2 against the inner surface of tube 26. Withthis constructioiithe fin assembly is expansible so that it is pushedby" the inner tube outwardly against the outer tube, but can not becompressed" to any great extent radially and, thereforeQthe fin assemblyis placed under radial compression by the expansion of tube 28. Thus,the fin assembly has good heat transierrelationship with both of thetubes and also witht he refrigerant flowing through the passageway 32between the tubes. Furthermore, the refrigerant now through thispassageway is relatively unobstructed because the fin extendlongitudinally of the passageway.

- In Figure} 2 the evaporator I9 is substantially identical-inconstruction with the condenser 2I,

' except that each of the tube assemblies has onits outer tube '3 a finassembly [I5 formed by s uare sheet metal II'I. These fins II! are putplace on each tube H3 prior" to assembly with its internal fin assembly36 andits inside. tube 28 and the tube 3 is xpmdd to hold iii) '6the-final I 1. inplace and. to give good: heat transfer relationship.The: refrigerant passes from the receiver'iithrough line I0andexp'ansionyalve I2 to the refrigerant inlet fitting 1 UL It; thenflows through the series of evaporatorpassaga ways identical withpassageways 32 to the re--' *fi-igerant outletfitting I I6 from which itreturns through line I5 to the compressor. An inlet fittin'g' I I 8'identical with fitting 35 on the condenser provides an inlet connectionfor a defrosting liquid which may be an aqueous solution cran otherliquid which is heated.

Thus, when frost accumulates on the evaporat tor the refrigerationoperation is discontinued.

and heated defrostingliquld is supplied to fitting This liquid flowsthrough the passageway corresponding" to the water passageway in; the

condenser and it is discharged at the bottom of the evaporator, througha fitting I26. The heat from the defrosting liquid passes through thewallsof tubes 28 and thence through the fin assemblies 3b to the outertubes 26. This heats the outer tubes and the fins so that theaccumulated frost or ice is melted free. It is thus seen that theevaporator surfaces arein good heat transfer relationship with theinside tubes 28 and, therefore, the defrosting operation is carried onefiiciently. This good heat transfer relationship exists by virtue ofthe fin assemblies 30 being held under radial compression so that eachfin assembly is in tight contact with the outer surface of its innertube and the inner surface of its outer tube. j

'Pte'ferring now again to Figure 1, it was stated above that thesecondary condenser I is of'speci'al construction and provides a heattransfer passageway for the return refrigerant. Referring to Figure 9;this condenser 1 is in many respects identical with condenser 2i ofFigure 2. There are six'tube assemblies I2 I-, each of which 156011!struoted in the same manner as tube'asseinblies of Figure 2 but theouter tube 28 carries a fin assembly I22 formed by fins I23whichare'identical with the fins "II'l on the evaporaton'of Figure 2.The headers I2 and I are quite similar to the. corresponding headers-22and 24 of Figure 2 and. differ only in. that certain of the partitionsor transverse walls are omitted and the right-hand header l25 is cutawayat the top.

Header I25 is formed by a set of interengaged channels I25, I28 and E32and thereis a single passageway I32 at the right between channels andI23 which is open. to the right-hand ends ofall of the tubes 28', exceptfor the top tube. There is also a single passageway [34 between channels[23 and I36 which is open totheannular finned passageways 32 between theooncentrictubes 2s and 28' of the respective tube assemblies. Header521i is similar to header H25 except that its channels extend to the topof the condenser and provide single passageway Ifili which is open. tothe left-hand, ends of all of the tubes 28 and a passage\vay .l38 which:is open to the lefthand ends of all of the passageways 3 2.

It has been. pointed out above that (see also Figure '.i) the compressedgas fiows from the compressor to the primary condenser 6 which, inactual construction, is mounted. at the side of the secondary condenserl and asingle fan passes air through the two condensers. The

refrigerant from the primary condenser passes through two tubes M9 and.I42 to the upper por- ;tion of passageway I38 at the left-hand end ofthe secondary condenser and, aswindicated, this 'to the intake port ofthe compressor.

-passageway is open to the left-hand end of all of the annular finnedpassageways 32 in the various tube assemblies. The bottom of thispassageway I38 is connected through a line 144 to the receiver and,therefore, the condensed refrigerant from the primary condenser flowsthrough the lines I40 and I42 into passageway I38 and down thispassageway and through line I44 to the receiver with minimum resistanceto flow. However, any refrigerant gas which is not condensed in theprimary condenser 6 separates from the liquid refrigerant in passagewayI38 and fiows into the various passageways 32 where heat is passed fromit by the internal fin assemblies 38 and also by contact with the outertubes 26.

The internal fin assemblies 38 are compressed as a result of theexpansion of the internal tubes action is performed by the secondarycondenser.

The secondary condenser is also a re-evaporator and the refrigerantreturns through it from the evaporator to the compressor. This return ie-evaporator passageway is formed by the inside tubes 28 and theinterconnecting passageways I32 and I36. Line i is connected to thebottom passageway I32 at the right-hand side of the unit and the toptube 28 has its righthand end connected to line #8 which extends Asindicated above, passageway I32 is connected to the right-hand end ofall of tubes 28 except the top one and the left-hand passageway I35 isconnected to all of the tubes 28. Thus, the refrigerant flowing fromline I5 into passageway I32 flows freely to the left through the fivelower tubes 28 and into passageway 138. From passageway I36 therefrigerant fiows to the right through the top tube 28 which is ofsufficient size to carry the refrigerant without objectionable pressuredrop. Thus, the refrigerant returning from the evaporator to thecompressor during the refrigeration cycle is passed into heat exchangerelationship with refrigerant on the high side. This not only insuresthat no drops or slugs" of liquid refrigerant will reach the compressorin the return line but it also improves the performance of the system.

During the defrosting cycle the fiow from the evaporator to thecompressor is unchanged and, as indicated, hot gas fiows through line I8directly to the evaporator where it melts ice or frost free. During thisoperation refrigerant is condensed in the evaporator and this fiowsthrough line I5 and valve I9, which then provides a pressure drop topassageway I32 and thence through the lower five tubes 28 to passagewayI36. The liquid refrigerant tends to 'fiow through the lower tubes whilethe upper "tubes 26 and the external fins I23. Therefore, heat isabsorbed by the fins I23 and passed by the internal fin assemblies tothe refrigerant in the inner tubes 28. The unit therefore acts as anefficient re-evaporator and insures the evaporation of all liquidrefrigerant which flows from the evaporator. The five tubes 28 operatein parallel and, as indicated, they ofier minimum resistance to therefrigerant flow. The top tube 28 prevents slopping over which mightoccur under some conditions of operation if line I6 were connected topassageway I36. Under some circumstances there may be one or moreadditional tubes connected in parallel with the top tube or a moreextended series arrangement may be provided so that the refrigerantfollows a longer path.

In the embodiment of Figure 3 an arrangement is shown schematicallywherein a single heat transfer unit I43 acts as an evaporator in. thesummer to cool the air in a room, for example, and acts as a heatradiator in the winter to heat the room. The unit I43 is identical withevaporator l9 of Figure 2 and the parts are correspondingly numbered.However, when the unit is acting as an evaporator its surfacetemperature'is above freezing and therefore frost does not form and itis unnecessary to defrost it.

For purposes of heating in winter the inner tubes 28 of unit I43 areconnected to a heating medium, illustratively, steam supplied from aremote boiler I41. The condensing unit of Figure 3 is identical withthat of Figure 2 except that a water cooled condenser I45 is providedwhich is identical in structure with evaporators I9 and I43. Incondenser I45 the inner tube circuit, formed by tubes 28 connected inseries, acts as a water circuit for the condenser cooling water the sameas in Figure 1 and therefore water is supplied to this inner tubecircuit through a valve I44 identical with valve 29 of Figure 2.However, each of the condenser tube assemblies is provided with externalfins as in Figure l, and under low load, conditions and at low ambienttemperatures, the cooling effect of the fins is sufiicient to condenseall of the refrigerant. Under such circumstances, valve I44 remainsclosed and there is no water flow because the pressure of the hot gasdoes not rise. However, at high loads and when the ambient temperaturerises the high side pressure rises indicating that the condenser is notcondensing the refrigerant; this opens valve I44 and permits water tofiow through the condenser so that there is auxiliary cooling. With thisarrangement it has been found that the unit can be designed for normaloperation as a solely air cooled unit; and yet peak and abnormal loadsneed not be taken into consideration insofar as the air cooling surfaceis concerned because such loads are handled with the assistance of watercooling. This arrangement is of particular advantage under circumstanceswhere the free use of water is objectionable and where maximumefficiency is important.

With the embodiment of Figure 3 the refrigeration system operates tocool the air during warm weather in accordance with the normalrefrigeration cycle of operation. During such operation the inner tubescarry no heating or cooling medium. However, they perform the functionreferred to previously of providing the high heat transfer relationshipbetween the fin structures and the outer tubes and thence with the air.When cooling is no longer required the refrigeration system is turnedoff and, if desirable, heating may be effected immediately by merelysupplying the heating medium such as steam to aoiiss i the f-ihner tubecircuit. "The steam or other heating mediurn such ashot'w'ater flowsthrough the inner tube circuit and the heat is transferred through thewalls of tubes 28 and thence through the-internal fin assemblies to theouter tubes 26 where it is transferred to the air. -'It is thus seenthat the refrigeration system-and the heat:

ing system utilize the sameheattransfer st um tures and yet the coolingfiuid andheating fluid circuits are not interconnected. in Figure 3 theto provide a high rate of heat transfer with theairas well as with thewater. Similarly, in the heat transfer-unit 43 high heat transfer isprovided-between-the refrigerant and the air in the summer and alsobetween the steam and the air in the winter-. Thus,- a single heattransfer unit of ininimumsize maybe provided with a single air.circulating and mounting structure. Under some circumstances hot wateror other hot nuid may be used as the heating medium and the fins may beomitted if the external surface is suihcientotherwise ;Geherally,transfer units-of the type herein disclosed are provided withfans whenthere is to bee heat transfer relationship with-air.- Thus, in theembodiments shown, fans are used whenever the tube assemblies areprovided with external fins.

With the various heat transfer units herein disclosed it will beappreciated that the header structures may be modified to obtain eitherfull parallel or full series flow, or there may be combined parallel andseries flow. For example, with a condenser the inner tubes may beconnected to operate with adjacent pairs in parallel or all of them maybe in parallel. Similarly, the passageways 32 may be connected so thattwo or three are in parallel. The particular internal fin structuregives minimum pressure drop through the passageways 32 even though thereis rapid flow. The pressure drop is, of course, reduced if parallel flowis provided, although under some circumstances, it is desirable toprovide an extended'series flow.

The arrangement of providing the internal fin structures with U-bends ofgreater mean radius at the outer tubes than at the inner tubes is animportant feature of construction. This the heat a characteristic of thefin structures is obtained by corrugating sheet metal with alternatewide and narrow U-bends. Thus, in actual production, a strip of sheetmetal having a width or transverse dimension which is exactly thatdesired as the length of the fin assembly is placed in a fin-formingmachine. This fin-forming machine has a sheet holder adjacent a formingzone at which the sheet is clamped originally with a leading edgeprojecting into the zone. Two forming strips of diiferent widths arepositioned on the opposite sides of the projecting leading edge of thesheet and they are moved edgewise into engagement with the oppositesides of the sheet. The engagement of the two forming strips is alongzones spaced slightly from each other and the movement of the formingstrips is continued so that the sheet is formed into two corrugations.One of the corrugations is narrower than the other because its formingstrip-is narrower and one whom! isalso harerower than the other;

The forming strips are then withdrawn and then the sheet is advanced andthe operation is then repeated until there is a 'sufiici'ent number ofcorrugations tor a 'fin assembly 30-. The an assembly is then curvedi'r'i'to annular formand edges are interlocked-as shown. inner tube asand a assembly 8c is then inserted into a tube =26 and in thisembodiment the inner tube 2'8 is expanded. Theexpansion is sufii'cientressxthe an assembly 30 outwardly'again s t the inner 'wail or tube 26and: each corrugation or fin ortion is placed. under compression. Undersome circumstances the outer tube may be us forrhed to a smallersize toobtain this com :rhe internal assembly i's 'd'eformable so that its meanradius 7 pressed condition bi -the nns.

may be changed readily or it may even be do formed toa shape so as toconform to the exact radial dimensionsor the space tim vided'ifor it.such deforming changes the totaii angles of the various ubends but theradially extending 'iinportions are hot bent materially;

Thus, the an assembly will, still withstand sub; stantial radialcompression which, in any event,

of the mechanical features of the above invention and as the art hereindescribed might be varied in various parts, all without departing fromthe scope of the invention, it is to be understood that all matterhereinabove set forth, or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

I claim:

1. In heat exchange apparatus of the type wherein a fluid is subjectedto a heat transfer operation, the combination of, a pair ofconcentrically positioned rigid members defining a sub-. stantiallyannular chamber for the how of the fluid to be subjected to a heattransfer operation, and an annular metallic fin assembly within saidchamber and comprising sheet metal corrugations each of which issubstantially straight and is non-distortable and extends longitudinallyof said chamber bridging the space between said rigid members and isconnected to the next adjacent corrugation by a trough-like connectingportion which presents a straight portion in contact with a surface ofone of said members, said trough-like connecting'portions providing theheat transfer contacts with the surfaces of said rigid members at theinner and outer peripheries of said annular chamber, said trough-likeconnecting portions at said outer periphery beingof substantiallygreater radius than those at said inner periphery, the distance betweensaid rigid members being such that each of said trough-like connectingportions is dismembers.

2. In heat exchange apparatus of the type wherein a fluid is subjectedto a heat transferop is substantially straight and is non-distortableand extends longitudinally of said chamber bridging the space betweensaid rigid members and is connected to the next adjacent corruga- V tionby a trough-like connecting portion which presents a straight portion incontact with a surface of one of said members, the trough-likeconnecting portions which contact the larger radius member being ofsubstantially greater radius than the trough-like connecting portionscontacting the lesser-radius member, the distance between said rigidcylindrical members being such that each of said trough-like connectingportions is distorted and each of said trough-like connecting portionsis subjected to substantial compressive forces which are applied at theinner and outer peripheries of said fin assembly by said rigid members.

3. Apparatus as described in claim 2 wherein said cylindrical memberscomprise inner and outer tubes, and a fin assembly positioned upon theouter surface of said outer tube.

. 4. Heat exchange apparatus as described in claim 3 which includes, apair of headers positioned at the respective ends of said tubes and eachproviding separate fluid connections to said inner tube and said annularchamber.

5. Apparatus as described in claim 2 whereinsaid cylindrical memberscomprise inner and outer metal tubes concentrically positioned and withtheinner tube being of greater length than the outer tube, and a heaterassembly mounting said tubes and comprising separate header meansproviding support and providing for the flow of separate fluids throughthe two chambers.

CECIL BOLING.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 660,202 Durr Oct. 23, 1900890,526 Numan June 9, 1908 907,084 McKenzie Dec. 15, 1908 1,584,772 HydeMay 18, 1926 1,585,671 Harms May 25, 1926 1,794,692 Hyde Mar. 3, 19312,003,122 Schwartz May 20, 1935 2,085,677 Thayer June 29, 1937 2,117,830Van Der Beyl May 17, 1938 2,206,826 Hopper July 2, 1940 2,415,865 BoothFeb. 18, 1947 2,526,032 La Porte Oct. 7. 1950 2,534,031 Kollsman Dec.12,1950 2,589,262

Keith Mar. 18, 1952

